Polymerization of olefins using early transition metal containing catalysts such as vanadium and zirconium is a well known and commercially important technology. In many instances it is desirable to lower the molecular weight of the polyolefin that would normally be produced. For example lower molecular weight polymers are usually considered easier to melt process, since they have lower melt viscosities. While polymerization process conditions can sometimes be altered to change the molecular weight of the resulting olefin, often a chain transfer agent such as hydrogen is deliberately added to the process to lower the polyolefin molecular weight.
The polymerization of olefins, especially ethylene and propylene, using iron or cobalt complexes of 2,6-pyridinecarboxaldehyde diimines or 2,6-diacylpyridine diimines containing catalysts, see for instance U.S. patent applications Ser. No. 08/991,372, filed Dec. 16, 1997 (now U.S. Pat. No. 5,955,555), and Ser. No. 09/006,031, filed Jan. 12, 1998 (now U.S. Pat. No. 6,150,482). However, methods for lowering the molecular weight of polyolefins produced in such processes are not known (except that decreasing the steric bulk of the ligand often results in lower molecular weight polymer).